The present invention relates to composite hollow cylindrical structures, more particularly to composite hollow cylindrical structures which are rib-stiffened and to filament winding methods for fabrication thereof.
Filament winding is a technique which is known in the art for the manufacture of cylindrical structures (e.g., tubes and pipes), spherical structures, and other surfaces of revolution. Typically, the filament winding process involves utilization of a resin bath through which dry fibers are passed and then wound; this type of filament winding is known as "wet winding." In this technique the wind angle, band width and tow tension are controlled. Incorporated herein by reference is an informative text on fiber composites: Agarwal, Bhagwan D., and Broutman, Lawrence J., Analysis and Performance of Fiber Composites, 2nd Ed., John Wiley & Sons, Inc., New York, 1990; see, especially, section 2.3.1.3 "Filament Winding," pp. 42-44.
Filament winding has been used by the United States Navy for various applications. For example, a wet winding procedure has been utilized by the U. S. Navy for the Advanced Unmanned Search System Vehicle (AUSS). The U.S. Navy has also utilized a wet winding procedure in the fi lament winding process for the manufacturing of the Composite Propeller Drive Shaft.
Manufacture of various types of composite structures having ribs or stiffeners is known in the art. In the manufacturing process for rib-stiffened flat structures, what is generally involved is the separate manufacture of the ribs and of the face sheets, followed by secondary bonding.
A rib-stiffened configuration has also been considered for cylindrical applications. A typical approach for achieving a rib-stiffened cylindrical design involves first winding ribs onto a mandrel which has rib grooves machined in it. After the ribs are wound or fabricated, the rest of the cylindrical form is wound. The mandrel, which is typically sectional, is then disassembled and the cylinder is removed. With this type of design, however, internal connections are made either to the ribs or the skin itself; hence, there is a direct path for vibration energy to propagate from the interior to the exterior of the structural form. This approach is thus deficient for applications in which maximization of energy dissipation from the inside to the outside of the cylinder is desired.
A process used in the filament winding of rib-stiffened cylinders which is similar to the one described above for flat shape applications is disclosed in a publication, incorporated herein by reference, from a 1986 Society of Manufacturing Engineers proceeding. See Harruff, P., Tsuchiyama T., and Spicola, F. C., "Filament Wound Torpedo Hull Structures," Fabricating Composites '86 Proceedings, Society of Manufacturing Engineers, Sept. 8-11, 1986, Baltimore, Md. This process requires the fabrication and curing of the skin and stiffeners, followed by the machining of the cylinder inner diameter and the rib outer diameter to high tolerance. After this is done, the ribs are carefully positioned and adhesively bonded to the skin. The materials used for the application disclosed by Harruff et al., it is noted, are a prepreg tape for the cylinder wall and a wet winding system for the ribs.
As aforementioned herein, wet winding procedures have been used by the U.S. Navy for the Advanced Unmanned Search System Vehicle (AUSS) and the Composite Propeller Drive Shaft. The AUSS was a cylinder of constant thickness and no ribs. See Technical Report 1245, August 1988, Stachiw, J. D., and Frame, B., "Graphite-Fiber-Reinforced Plastic Pressure Hull Mod 2 for the Advanced Unmanned Search System Vehicle," Naval Ocean Systems Center, San Diego, Calif., incorporated herein by reference; see therein, especially, pages 16-21, and FIG. 18 on page 54 therein ("Schematic of Winding Operation"). For the manufacture of the Composite Propeller Drive Shaft, dry tows are passed through a resin bath to coat the tows. After tow impregnation they are fed onto the mandrel at various orientations to achieve the desired part. Incorporated herein by reference is Report No. DTRC-PASD-CR-1-88, Contract No. N00167-86-C-0150, Tulpinsky, Joseph F., and May, Marvin C., "Filament Winding Process for Composite Propeller Drive Shaft Sections," October 1986 to October 1987, prepared by Hercules, Inc. for David Taylor Naval Ship R & D Center; see, especially, pages 4-1 through 4-8 therein (Chapter 4.0 "Manufacturing").
The U.S. Air Force used the filament winding technique for the B-1B composite Rotary Launch Tube. Here the winding process utilized prepreg tape in favor of the wet winding technique in order to achieve a tighter control on fabricated properties. Incorporated herein by reference is Peters, S. T., Humphrey, W. D., and Foral, R. F., Filament Winding, Composite Structure Fabrication, Society for the Advancement of Material and Process Engineering, Covina, Calif. 1991; see, especially, pages 2-9, 2-12, 11-1 to 11-3.
Although the above-described processes for manufacturing bodies of revolution have achieved satisfactory results, they have generally been discontinuous and time-consuming and have required precision equipment and machining.